


Song of the Sea

by Kestrealbird



Category: Final Fantasy XV
Genre: Dad Ardyn, Found Families, Gen, JOSE LOOK ITS THE THING, M/M, Slow-burn PromNyx, everyone appears at some point, mermaid au, protective Ardyn, rating my change, siren au
Language: English
Status: In-Progress
Published: 2017-03-11
Updated: 2017-04-18
Packaged: 2018-10-02 13:30:03
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 2
Words: 4,828
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10219382
Author URL: https://archiveofourown.org/users/Kestrealbird/pseuds/Kestrealbird
Summary: Prompto has always been told to keep his heart sheltered and avoid falling in love. He'd only get hurt in the end after all. But as he gazes at Nyx Ulric he wonders if the beating of his own heart will allow him to follow that advice.





	1. The Beginning

**Author's Note:**

  * For [Lyrecho](https://archiveofourown.org/users/Lyrecho/gifts).



> OMG guys this is going to be LONG. I cant believe I'm actually writing this lmao hope I do my own AU justice. Also who ever though they'd see an AU where Ardyn is a good dad? Not me but here we are so buckle in my dudes.

_ A Siren's trust is hard to earn _

_ Their love is even harder _

_ And when that trust or love is burned _

_ A Siren then shall murder _

“What a load of Sailor’s shit,” he tossed the book haphazardly away from himself and scoffed at the words, “We can't murder those we use to love so easily. We suffer for a good many years first. Stupid humans.” He clicked his tongue and glided through the water to fetch his hat and coat, his scarred maroon tail curling to try and avoid causing him anymore pain than he already felt. 

Making a pleased sound at his appearance, he twisted through his cavern and lazily made his way to the nearest food source. He didn’t particularly like eating humans who weren't fresh kills, but the sea had been treacherous recently, so unless he was desperate enough to eat the common fish, he’d have to do with this for now. Humans and their silly weak spirits. Honestly it was just a storm or two, so what if they lost some good men? They should learn to take the risk more often. 

He stopped and frowned down at where his meal should be, only to narrow his eyes when he found it was nowhere to be seen. 

Thieves weren't a common occurrence in his territory, mostly because they knew not to try and steal from him specifically, but these things happened sometimes. He’d just have to teach them what happens to thieves here the hard way. Mer-folk weren't the only one with claws and fangs. 

The thin trail of blood was easy to follow -the fool of a thief hadn't thought to try and be more discreet- and he flexed his clawed hand, prepared to tear out this one's throat if he had to.

He wasn't prepared for the scene that lay before him.

A young Siren -barely a child- sat there, struggling to get food down his throat and a thick chain was wrapped around their neck and wrists. The poor child was clearly starved and had no idea how to properly eat, let alone anything else. Slowly and carefully he approached the child and was mildly pleased to see how the other dropped the meal and tried to hide in the shadows. A poor effort, but at least the young one understood what danger was.

He let out a soft trill, a sign that he meant no harm, and was enraged to see the child cower even more. Someone had used the Siren tongue to hurt this child and Ardyn would be damned if he let such an offense slide so easily. Gently he sat down on a rock a short distance away from the child, and tore off some of the meat from his kill. He threw it just in front of the other, and patiently tore off and ate his own piece. He did this for a while, and watched as the child cautiously approached the food, and attempted to mimic his movements. It was….endearing, in its own way. 

The child's movements were uncoordinated and he found himself offering sharp clicks to help teach them how to feed. They hesitated the first few times, but eventually realized he was  helping and cautiously listened to his advice. He trilled again, softer this time, and the child tried to respond. Their hands touched the chain around their neck and they looked close to tears.

They couldn't speak the song. Not like this.

He glided over and gently placed his hands over the child’s own. He gave them an understanding look and carefully moved their hands so he could see the chain up close. It dug painfully into the child’s skin, and if not removed it would leave permanent scarring. He ignored his instinct to just bite and tear through the chain with his teeth, so as not to scare the poor thing and instead opted to softly untangle the chain, and let it fall to the ocean floor. 

The child stared at him with wide-eyes and slowly touched their neck. He trilled again and this time they managed to give him a response. It was warped and hoarse, without an accent and hard to understand, but he was proud nonetheless and nodded his approval. The child hesitantly held out their wrists and he wasted no time in getting rid of those chains too.

A horrific barcode stared up at him and he hissed when he saw it, resisting the urge to gather the child in a hug and cover them with his coat. He looked around briefly and grabbed some seaweed before tying it around the child's wrist. He would find something better later on, but this would do for now. There were more wounds to take care of and he noticed some scarring on the child's torso, the kind you got from being electrocuted continuously. 

The child looked up at him and he saw a glint of hope in their eyes. His gaze softened and he hummed a small tune. The child reached out and clung to his coat, looking up at him in question.

“We all have names,” he said, “Mine is Ardyn. So what is yours?” He tilted his head and the child opened their mouth, reciting the numbers on their wrist. Ardyn tutted. “That won't do at all.” He muttered and the child looked confused. He didn’t exactly want to get into that conversation right now so he went for an easier explanation, “that sort of thing would be too hard for anyone to remember, let alone call you,” he rubbed his chin in thought and then snapped his finger. “Prompto,” he said, “that will be your name.”

The child looked up at him and frowned in concentration. They attempted to sound out the name but gave up after their fifth try and Ardyn chuckled. They would get there eventually. He looked at the child’s eyes and noticed that they were sharp, but not narrow. Prompto was a boy then. Female Sirens would have the wide doe-eyes of an innocent virgin (a lie of course, just to lure the food in better) or the narrowed eyes of a temptress. 

“We still have a meal to finish.” Ardyn wrapped his arms around Prompto and felt the boy beginning to freeze up, as if expecting some kind of blow. He vowed to gut the ones who had hurt the boy like this and gave another comforting trill. The first thing he needed to do, was teach this child how to be a Siren. He wouldn't be a father, just a caretaker. Neither of them needed to have that sort of  _ familiarity  _ and emotional commitment. Not right now at least, if ever at all. 

They sat together and ate in relative silence, Ardyn teaching Prompto small sounds and songs, chuckling whenever the child got frustrated at his own lack of skill. For the first time in a long time, Ardyn felt affection fill his heart and hummed a Siren’s Lullaby.


	2. The Only Way is Up

**Summary for the Chapter:**

> Prompto has some new experiences and Ardyn begins to feel an emotion he long since banished from his soul.

It’s not like he’d expected this whole thing to be easy. Just taking in a Siren child was responsibility enough, but to look after one who had been abused….

He sighed. As much as Ardyn wanted to just wave a magic wand (stupid human conception but interesting stories nonetheless) he knew that such a thing wasn't possible. He’d have to simply take his time and slowly show Prompto that he could be trusted. Starting by getting the boy used to sleeping on a soft bed instead of the rocky ground.

He looked down at the boy as he attempted to get somewhat comfortable on the hard ground and knelt down next to him. Prompto looked nervous and stilled in his movements, perhaps believing he’d done something wrong and was going to be punished, but Ardyn simply gave a sad smile and shook his head. 

“Do you not want to sleep on a bed?” He inquired. Prompto’s eye flickered between the bed and Ardyn before he shook his head ‘no’ and curled his tail further around himself. Ardyn huffed a breath and lay next to him. He propped his chin onto his hand and looked at Prompto expectantly. Prompto hesitated, and then he slowly lowered himself to curl up on the cavern’s floor. He shivered a little and Ardyn tutted before opening his coat and placing it around the child. 

Prompto looked at him for a moment and Ardyn hummed. He closed his eyes and nestled into his arms. Ardyn smiled, a soft look gracing his features. It wasn't much, but it was progress. What was it humans say? ‘Little steps’? Yeah. He could work with this.

~

Ardyn woke to the sound of soft sniffles and balanced himself on his elbows, hat forgotten on the floor, as he looked for the sound. 

His eyes landed on Prompto, huddled in a corner and quietly sniffling. Frowning, Ardyn glided towards him and gave a questioning click. Prompto jolted, and with a fearful expression tried to back away from Ardyn. He floated down and sat just a few feet away, waiting to see how Prompto would react. The child considered him for a moment and then, quietly, with a voice clearly not used to being used, he said “I’m so...rry.”

He gave Prompto a questioning look and the boy quietly said, “touched….you.”

Ardyn’s face went blank. “What?”

Prompto trembled and bit his lip. “Warm…” He sniffed again.

Oh.

OH.

Ardyn sighed and gave a smile. “If you’re cold it’s only natural that you’ll move to something warm,” he stretched out with a soft groan and Prompto gave him a nervous and quizzical look, “you did nothing wrong. So do you want to stay up or go back to bed?”

Prompto looked down for a moment and then, quietly, “Can cuddle?” he sounded so hopeful and Ardyn couldn't say no. He wasn't the type of person who enjoyed physical contact, but if it helped the boy then he would simply have to resign himself to being more….affectionate. Besides, he really needed to help Prompto learn how to use his vocal chords.

“Cuddling is fine,” he said, “but I’d prefer if you waited for me to sleep first. I’m not quite used to physical contact myself.” He grinned and made a proud chirp sound as Prompto silently shook with laughter.

Prompto’s laughter died down and he shyly twiddled his thumbs. “Not hit?” He asked, so soft that Ardyn could barely hear him. 

Ardyn gazed softly at him and a reassuring smile helped ease the child’s nerves. “No,” he whispered, “you won't get hit. Not ever. Not by me.” A hard promise to keep, but he would keep it nonetheless. Prompto nodded and Ardyn gestured back to his coat. It didn’t take much to convince Prompto to go back to bed, and Ardyn was amused at the way the child shimmied under his coat and curled up in the warmest spot he could find.

Ardyn shimmied under the coat himself, and adjusted it to tuck them in better. Laying under his coat like this reminded him of the time he spent with Regis….

No. He wasn't going to think of that merfolk here. Not now. Not after all these years when he’d finally started getting over the heartache. The feel of someone nuzzling into his arms caused him to freeze up momentarily, before he remembered it was only Prompto. He huffed. So much for waiting until he was asleep. Wrapping an arm around the child, Ardyn pretended it was only so he could sleep better and ignored the purr in his head.

_ My child _

Not his. Just someone he was looking after. That was all.

~

If getting Prompto used to sleeping in a bed was hard then teaching him to eat was just…..

Ardyn took a deep and calming breath. He needed an award for not just rushing off to blindly slaughter whoever hurt this kid. Preferably make the award some kind of alcohol. Rum was nice. 

Ardyn gave a soft and sharp click, effectively stopping Prompto from almost tearing out his own teeth, and moved the kids hands to show him how to tear off muscle without hurting yourself. Digging his claws into the flesh, just behind where the muscle was, Ardyn made a careful incision and then waited for Prompto to do the same on the opposite side. The boy’s incision was messy and not nearly as neat as Ardyn’s own, but he didn’t expect any different for a first attempt. He helped Prompto grab the muscle with both hands and then steadily showed him how to tear it out, the two incisions making the process much easier then just biting and yanking full force. 

Prompto twisted the muscle around in his blood-stained hands and frowned, unsure with how to proceed. He’d probably only been fed on scraps or something. Ardyn gave another sigh -probably the hundredth one today, including the ones reserved for his theatrical performances- and then patiently clacked his teeth together, effortlessly getting Prompto to pause in his movements. 

The child may not know how to create such sounds himself yet, but he at least knew what the basic meaning behind them was. He took some muscle for himself, and then turned it so the softest part faced him and bit down, allowing the blood to run down his throat as he drank it up, effectively making the muscle limper and easier to bite and chew into (it had less flavour like this, but he would make the sacrifice to let the kid actually  _ eat  _ for once). Prompto mimicked his actions, fumbling with his food for a few moments, and then when he bit in and drank the blood, a pleased groan escaped him. The blood dribbled down his chin and arms, but he was a lot cleaner than Ardyn had expected. 

A quick learner, which meant he was highly observant and would become a good hunter in time. His vocals still needed work, but right now Ardyn was more concerned with helping the kid get his strength and health back up. He’d have preferred getting a meal with more….fat on it, but without the seals here there wasn't much variety. He did not want to get something too small or soft, they wouldn't have enough protein for the boy at the moment, and would do very little in filling him up. 

“Eat slower so you don't choke,” Ardyn murmured absentmindedly and Prompto slowed his chewing. They ate like that for a while and after the third time being corrected in his eating habits, Prompto was a lot more patient and calm by the end of it. Most likely he finally realized that Ardyn wasn't  going to suddenly whisk his food away and let him starve. A foolish notion really, but given his circumstance Ardyn couldn't fault him for it. Speaking of, he really needed to find something better to cover the boy’s wrist with. Seaweed and kelp could only go so far, and Prompto’s wrist would start to itch and get irritated after a while. 

A Siren's skin was either overly sensitive or barely sensitive at all. Prompto was looking to be the former and Ardyn himself was the latter. Already he was imagining the different ways he could ‘persuade’ Prompto’s future suitors to leave him be. Damn. He was growing too soft in his old age it seemed.

Prompto looked at him silently and with a patient sound -somewhere between a growl and a purr- Ardyn told him he could speak. 

“...tail….colour?” He tilted his head and pointed from Ardyn’s maroon tail to his own plain grey one. 

Ardyn gave an amused chuckle and gave a grin that was just short of being all teeth. “Your tail will change colour when you’re older, it may not be as beautiful as the tails of other aquatic creatures, but the simple colours help our prey to focus on our voices, instead of the vanity of a bird fluffing its feathers.” Prompto snorted and Ardyn’s grin faded to a fond smile. “All Siren tails start off as a plain grey, you’ll get colour soon enough, no need to be impatient.” He wagged a finger at the child and Prompto nodded, allowing himself to almost grin. 

A string of excited chirrups escaped Prompto’s mouth as he flailed his arms and imagined all the colours his tail might become. Ardyn clicked his tongue and Prompto settled down, tilting his head in confusion.

“I can't understand a word you’re saying,” he held up a finger to stop Prompto from interrupting, “Our voices and songs display emotions, however, we cannot communicate in full sentences with them. It’s the reason we still use  _ words _ Prompto.” The boy winced and nodded. “Good. Now please, try to speak,” he gestured to the boy and waited.

Prompto’s eyes flickered before he took a deep breath and opened his mouth. “Loads…..of...colours,” he enunciated each word slowly, his voice hoarse and croaking slightly, but his eyes shone in delight regardless, and Ardyn gave a pleased purr. “Your tail….colour?” He leant forward and Ardyn was sure that if he had feathers he would’ve fluffed them up in pride.

“Maroon,” he stated. Prompto mouthed the word a few times and then giggled.

“Maroon!” He chirped. Ardyn was startled for a moment, but then he smiled and calmly licked the blood from his fingers.

“Clean yourself up,” he said. Prompto blinked and then blushed before hastily doing as he was told. “You can speak whenever you wish you know,” he said and watched as Prompto stilled, waiting for the joke to appear. When it was clear that Ardyn was serious, he looked up at the older Siren through his bangs and gave a small grateful smile. 

“Care for a swim outside?” He pointed to one of the many tunnels and Prompto considered the offer. He gently took hold of Ardyn’s coat, a silent yes, and allowed himself to be slowly led to the exit. 

The tunnels twisted and turned, and there were many different rooms, some had doors and others didn’t. They passed one of the rooms and Prompto took note of three things. One: the door was regal and had a strange design to it. Two: It was the only door that was locked and clearly not meant for anyone’s prying eyes. And three: Ardyn stiffened and subtly moved away from it as they passed, almost as if it pained him to be near the room. Prompto resolved to ask him about it one day, and if he didn’t wish to speak of it then that was fine. It wouldn't change anything. But if he did, then they would be just that little bit closer. Prompto hoped that it was the latter.

It was a shame that he didn’t get a chance to look at the door for longer; he might have noticed that a five letter name had been scratched out, leaving behind two letters you could barely see.

E and I.

~

Prompto stayed close to Ardyn while they glided through the water, never once letting go of the man’s coat and keeping an eye out for any potential threats. He knew, subconsciously, that Ardyn could do that himself, but it helped Prompto feel safer and more useful. Ardyn didn’t seem to mind and even gave him a few hints to help him figure out what could be a threat and what was insignificant.

“If you feel like someone is watching or hunting you, don't let on to your discomfort or fear. Let them think they have you cornered and then lead them to an area where you have the advantage. Strike when they least expect it if you can.” Ardyn stopped moving, and turned to Prompto, his voice soft, “I won't always be there to help you, as much as I would prefer that you lead them to me, you’d do well to learn how to fight for yourself. Not yet of course, but in time.”

Prompto pursed his lips before saying a quiet, “okay.”

They swam in relative silence after that, silence only broken by Prompto mimicking and learning the Siren Song. 

“Did you know that ‘Siren’ is used for the individual?” Ardyn spoke suddenly and Prompto jerked in surprise. “If you want to address us as a species or a group the term we, as Sirens, use, is ‘Sera’.” The word was more sung than spoken, and the notes used were incapable of being replicated by other creatures. Prompto tried it out and failed spectacularly at the pronunciation.

Ardyn laughed at him. “It is not a word that's easily learned Prompto. Children your age won't be able to pronounce it for another 3 years or so, when your Vocal Chords develop properly.”

Prompto pouted. How unfair.

They came to a stop at a forest of seaweed and kelp that rose higher than Prompto could see, and he immediately knew that this was the border of Ardyn’s territory. 

Ardyn motioned for Prompto to look somewhere and when he did he opened his mouth in silent awe. A creature similar to them but with more extravagant features was swimming by and he turned to Ardyn with sparkling eyes.

“A merperson,” Ardyn supplied, though he was sure Prompto had already guessed as much. “They’re an AngelFish I believe.” 

This merperson was very thin and their tail was flat and elegant. They had 3 gills on either side of their face; one on the cheek, one under their jaw line and the last one on their neck. A fin was on their back and their hair was short. The merperson had thin fins that split in two protruding from their elbows. The underside of their tail was white, the sides were black and the top was a creamy brown. Their skin was the same colour as their tail and they looked extremely delicate. AngelFish suited them.

“Name….?” Prompto watched the merperson slowly swim in delicate patterns as he asked Ardyn.

“Vinny, if I remember correctly,” he replied and gave a respectful nod at Vinny when they caught his eye. Vinny nodded back and then continued swimming in patterns.

“What are….they doing?” Prompto tilted his head in question as he watched Vinny make pretty patterns in the water.

“Hmm if I remember they’re waiting for-” he stopped and nudged Prompto. “For him I believe.” Prompto looked in the same direction as Ardyn and saw another merperson swimming forward. When the two caught sight of each other, the other merperson blew Vinny a kiss and Vinny gave a flirtatious wink back. 

They swam quickly to one another and started talking excitedly. Prompto was too far away to hear them.

“Name?”

“Viktor. They us he and they pronouns I believe.”

Prompto looked over at Viktor and took in his appearance. Like Vinny, Viktor was quite thin but his tail looked more like a wide flowing fan then anything. His tail was a mix of blue, red and purple and the scales stretched up his spine and curled around his neck like a choker, falling between his collarbones. He had small gills on his neck and a short fin on each elbow. Short hair framed his face and when the sunlight hit his scales they reflected like a jewel. 

Prompto gave an awed sound and Ardyn barked out a laugh. Viktor and Vinny cooed at the sight of Prompto and then raced each other across the ocean.

“Don’t ask me where they’re going because I have no idea,” Ardyn said before Prompto could think to do so.

He puffed out his little cheeks and if Ardyn were a lesser man he might have squealed at the sight. But he wasn't so he didn’t. 

Ardyn gave him a thoughtful look and then hummed. “Tell me, do you know what a reflection is?” Prompto mouthed the word with a frown and creased his brows. He shook his head. Ardyn looked up to the surface. “It’s when you look into something like the water, or glass perhaps, and you see yourself staring back,” his eyes flickered to the child and he saw Prompto’s curiosity. “Do you want to see yourself?”

He thought it over for a few minutes, then bit his lip with a short nod. Ardyn took off his coat, leaving him in a vest and shirt, and wrapped it around Prompto. 

“It’s going to get colder up there,” he explained simply.

It only took a few minutes for them to swim up to the surface, and when they broke through the water Prompto scrunched his face up at the sensation. He looked down at the water and was startled to see himself staring back. So this was a reflection…

He looked at his blonde hair, his own blue-violet eyes, the fair colour of his skin and the markings that littered his face and body. He pointed to them in wonder and Ardyn chuckled.

“They’re called freckles.”

“Pretty….” Prompto whispered. He undid Ardyn’s coat so he could see the markings on his stomach, the ones left from the electric that was used to strike him…. He frowned and quickly covered himself back over.

“You know, those scars look very similar to what humans call stretch marks,” he hoped that Prompto wouldn’t hate the scars forever but he wasn't surprised when Prompto shook his head fiercely and refused to show the scars again.

“We’ll need to get you some clothes,” Ardyn murmured and Prompto sighed at the thought of wearing something as soft as this coat again.

~

“Come back soon ya here!” 

Ardyn waved at the old turtle mermaid with her seaweed hair and barnacle covered shell as they left her little clothing shop. Prompto had been instantly enamoured by the place and the old lady had given Ardyn a raised eyebrow when she’d seen him with a child. Thankfully she chose not to comment and simply went about making some clothes for the boy. Prompto was now proudly wearing a hooded top with a picture of a seadragon on the front and back, and his wrist was covered with a leather band that had a simple but effective buckle. For an old turtle she was rather quick and efficient with her work. 

She also felt disgusted that he still wore ‘that ragged carpet’ as a coat. But it had been a gift and now it was simply a part of his character so he refused to do away with it. Despite her disgust with the coat, Monica had never asked him to throw it away -she understood the attachment to it- and simply fixed it up with a frown and a grumble whenever he got it torn up. He was grateful for this much, at least, even if she was still a citizen of  _ that man’s _ kingdom.

Prompto looked up at him with eyes that glowed in the dark waters and Ardyn’s bitterness faded into a soft feeling he would rather not put a name to. “I like Miss Monica!” He said it so brightly that for a moment Ardyn thought he’d been possessed by another child, but the eyes glowing faintly at him were definitely Prompto’s. He felt pride and another soft feeling that he quickly squashed down.

“She’s an interesting one for sure,” he agreed. Ardyn turned to stare longingly at a sea current. What he’d give to dive in and let himself be carried along back home. But Prompto was still young and unsure, it would do no good for him to panic whilst still in such a fragile state.  He turned his eyes back down to the child and said, “shall we go home them?”

Prompto nodded and Ardyn wasn't blind to the slight confidence that wove around the child’s shoulders.

~

Quietly, Ardyn slipped out of his clothes and placed his coat on the floor, prepared to crawl under it like last night, before Prompto stopped him and nervously started wringing his hands.

“Is something wrong?” He waited as Prompto opened his mouth a few times to answer before closing it again. 

“Can we….sleep…..” He pointed to the bed shyly and Ardyn smiled in reassurance. 

“Of course Mo Stór.” He gathered his coat up and gently laid it on the bed. Prompto shimmed under it and curled up almost immediately, exhaustion clear on his features. Ardyn chuckled before joining him there. “ Tomorrow,” he said, “I’ll take you to see a different type of Sera.”

Prompto blinked tiredly at him. “Different type…?” He yawned and Ardyn chuckled as he reached over to ruffle his hair.

“You’ll find out tomorrow.”

“...ok…” Prompto breathed and then he closed his eyes and fell asleep to the feel of Ardyn’s fingers in his hair. 

Tomorrow would be a new day that they were  _ both _ looking forward too. Ardyn’s eyes slipped closed, and this time he was too tired to squash down the feeling of pure  _ love  _ that began to bloom in his heart.

**Notes for the Chapter:**

> PHEW! Finally got this chapter done! My friends Vinny and Viktor made a guest appearance here because I love them! Just a side note but Mo Stór means 'My Treasure' in Irish Gaelic and is used as an endearment with friends, family and children!


End file.
